Design and Construction of a Fusion Peptide Containing B1, B2, B4, and EPC1 Epitopes for Diagnosis of Human Cystic Echinococcosis

Abstract

Background: Cystic echinococcosis (CE), larval stage of Echinococcus granulosus, immunodiagnostics is still a challenge due to asymptomatic nature of CE during the early phase of infection and imperfection of diagnostic antigens. In silico design and assessments of hydatid cyst antigens provide preeminent information for novel and favorable diagnostic methods. Methods: This study was performed at the Tehran University of Medical Sciences, Tehran, Iran in 2018. The sequences of B2, EPC1, B1 and B4 antigens were collected and analyzed for sequence conservancy by protein BLAST search and CLUSTALW multiple sequence alignment. The secondary and 3D structures were predicted using ab initio and threading methods. The antigens were analyzed for their B cell epitopic content using linear and conformational B cell epitope prediction tools. The final diagnostic antigen was designed by fusing the selected epitopic determinants form each antigen. Results: Given the conservancy results and B cell epitope predictions, the whole B2 antigen along with amino acids spanning 1-50, 1-30, and 30-81 regions of EPC1, B1 and B4 antigens were selected to design the final antigen. High surface accessibility (75%), protein stability, low free energy and high number of amino acids involved in B cell epitopes were desirable properties for the final antigen to interact with antibodies against CE. Conclusion: In silico design of such antigens is useful for better diagnosis of CE, decrease the cost and the time required for antigen design, while avoiding the ethical aspects of in vivo studies.